Contents
NEET Physics Chapter Wise Mock Test – Electromagnetic Induction
Question 1:
A fan blade of length 1/√π metre rotates with frequency 5 cycle per second perpendicular to a magnetic field 10 T. The potential difference between the centre and the end of the blade is
(a) -50 V
(b) +50V
(c) -2 V
(d) +0.02 V
Question 2:
In a uniform magnetic field of induction B, a wire in the form of semi-circle of radius r rotates about the diameter of the circuit with angular frequency ω. If the total resistance of the circuit is R, the mean power generated per rotation of rotation is
Question 3:
A square of side L metres lies in the xy plane in a region, where the magnetic field is given by B=B0 (2i+3j +4k) T, where B0 is constant. The magnitude of flux passing through the square is
(a) (2B0L2) Wb
(b) (3B0L2) Wb
(c) (4B0L2) Wb
(d) (√29 B0L2) Wb
Question 4:
A loop, made of straight edges has six corners at A (0,0,0), B(L,0,0),C(L,L,0), D(0,L,0), E(0,L,L) and F (0,0,L). A magnetic field B = B0(i + k) T is present in the region. The flux passing through the loop ABCDEFA (in that order) is
(a) B0L2 Wb
(b) 2B0L2 Wb
(c) √9 B0L2 Wb
(d) 4B0L2 Wb
Question 5:
The magnetic flux linked with a coil varies with time as Φ= (3t2 + 4t + 9) Wb. What is the induced emf at t= 2s?
(a) 3 V
(b) 4 V
(c) 9 V
(d) 16 V
Question 6:
As a result of change in the magnetic flux linked to the closed loop shown in the figure, an emf V volt is induced in the loop. The work done (joules) in taking a charge q coulomb once along the loop is
(a) qV
(b) zero
(c) 2qV
(d) qV /2
Question 7:
A cylindrical bar magnet is rotated about its axis shown in figure. A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then,
(a) a direct current flows in the ammeter A
(b) no current flows through the ammeter A
(c) an alternating sinusoidal current flows through the ammeter A with a time period T = 2π/ω
(d) a time varying non-sinusoidal current flows through the ammeter A
Question 8:
The magnetic flux through a surface varies with time as follows
Φ= 12t2 +7t – 3
Here, Φ is in milliweber and t is in seconds. What will be the induced emf at t = 5 s?
(a) 338 mV
(b) 127 mV
(c) 105 mV
(d) None of these
Question 9:
Question 10:
A square loop of wire of side 5 cm is lying on a horizontal table. An electromagnet above and to one side of the loop is turned on, causing a uniform magnetic field downward at an angle of 60° to the vertical as shown in figure. The magnetic induction is 0.50 T. The average induced emf in the loop, if the field increases from zero to its final value in 0.2 s is
(a) 5.4x 10-3 V
(b) 3.12x 10-3 V
(c) 0
(d) 0.25 x 10-3 V
Question 11:
The flux linked with a coil at any instant t given by
Φ= 10t2 -50t+ 250
Then, induced emf at t = 3 s is
(a) -10V
(b) 10V
(c) 190V
(d) -190V
Question 12:
A non-conducting ring of radius r has change per unit length lambda. A magnetic field perpendicular to plane of the ring changes at rate dB/dt. Torque experienced by the ring is
Question 13:
A coil having n turns and resistance R Ω is connected with a galvanometer of resistance 4R Ω. This combination is moved in time t sec. From a magnetic field (W1) wb to (W2) wb. The induced current in the circuit is
Question 14:
A copper ring having a cut such as not to form a complete loop is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring, as shown in figure. The acceleration of the falling magnet is
(a) g
(b) less than g
(c) more than g
(d) zero
Question 15:
The current from A to B is increasing in magnitude. What is the direction of induced current, if any in the loop as shown in figure.
(a) No current is induced
(b) Clockwise current
(c) Anti-clockwise current
(d) Alternating current
Question 16:
Three identical coils A, B and C are placed with their planes parallel to one another. Coils A and C carry currents as shown in figure. Coils B and C are fixed in position and coil A is moved towards B. Then, current induced in B is in
(a) clockwise current
(b) anti-clockwise current
(c) no current is induced in B
(d) current in induced only when
Question 17:
The magnet in figure rotates a shown on a pivot through its centre. At the instant shown, what are the directions of the induced currents
(a) A to B and C to D
(b) B to A and C to D
(c) A to B and D to C
(d) B to A and D to C
Question 18:
When a coil of cross-sectional area A and number of turns N is rotated in a uniform magnetic field B with angular velocity ω, then the maximum emf induced in the coil will be
(a) BNA
(b) BAω/N
(c) BNAω
(d) Zero
Question 19:
A bicycle wheel of radius 0.5 m has 32 spokes. It is rotating at the rate of 120 revolutions per minute, perpendicular to the horizontal component of the earth’s magnetic field BH=4×10-5 T. The emf induced between the rim and the centre of the wheel will be
(a) 6.28×10-5 V
(b) 4.8×10-5 V
(c) 6×10-5 V
(d) 1.6×10-5 V
Question 20:
A conductor of length l and mass m can slide along a pair of vertical metal guides connected by a resistor R. A uniform magnetic field of strength B normal, to the plane of page is directed outwards. The steady speed of fall of rod is
(a) mgR/B2l2
(b) mg/b2l2R
(c) B2l2/mgR
(d) mgB/l2R
Question 21:
A uniform but time varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper as shown in figure. The magnitude of induced electric field at point P at a distance r from the centre of the circular region
(a) is zero
(b) decreases as 1/r
(c) increases as r
(d) decreases as 1/r2
Question 22:
Two coils of self-inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is
(a) 10 mH
(b) 6 mH
(c) 4 mH
(d) 16 mH
Question 23:
The coefficients of self-induction of two coils are L1, and L2. To induce an emf of 25 V in the coils change of current of 1A has to be produced in 5s and 50ms, respectively. The ratio of their self-inductances L1: L2 will be
(a) 1:5
(b) 200:1
(c) 100:1
(d) 50:1
Question 24:
The variation of induced emf (E) with time (t) in a coil, if a short bar magnet is moved along its axis with a constant velocity is best represented as
Question 25:
When the current changes from + 2 A to – 2 A in 0.05 s, an emf of 8 V is induced in a coil. The coefficient of self-induction of the coil is
(a) 0.1H
(b) 0.2H
(c) 0.4H
(d) 0.8H
Question 26:
In a solenoid, if number of turns is doubled, then self-inductance will become
(a) half
(b) double
(c) 1/4 times
(d) quadruple
Question 27:
The current in a coil changes from + 10A to – 2A in 3ms. What is the induced emf in the coil? The self-inductance of the coil is 2 mH.
(a) 8V
(b) 4V
(c) 0.8V
(d) 0.4V
Question 28:
Two coils X and Y are placed in a circuit such that a current changes by 3A in coil X and the magnetic flux changes of 1.2 Wb occurs in Y. The value of mutual inductance of the coils is
(a) 0.2H
(b) 0.4H
(c) 0.6H
(d) 3.6H
Question 29:
The cause of production of eddy currents is
(a) the motion of a conductor in a varying magnetic field
(b) the motion of a insulator in a varying magnetic field
(c) current flowing in a conductor
(d) current flowing in an insulator
Question 30:
Magnetic flux in a circular coil of resistance 10 Ω changes with time as shown in figure. Direction indicates, a direction perpendicular to paper inwards, match the following columns.
Direction (Q. Nos. 31-35): In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
(a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
(b) If both Assertion and Reason are true but the Reason is not correct explanation of the Assertion
(c) If Assertion is true but Reason is false
(d) If both Assertion and Reason are false
Question 31:
Assertion (A): The mutual inductance of two coils is doubled, if the self-inductance of the primary or secondary coil is doubled.
Reason (R): Mutual inductance is proportional.to the self-inductance of primary and secondary coils.
Question 32:
Assertion (A): Making or breaking of current in a coil produces no momentary current in the neighbouring coil of another circuit.
Reason (R): Momentary current in the neighbouring coil of another circuit is an eddy current.
Question 33:
Assertion (A): A coil A is connected to a voltmeter V and the other coil B to an alternating current source. If a large copper sheet C is placed between the two coils, the induced emf in coil A is reduced.
Reason (R): Copper sheet between the coils has no effect on induced emf in coil A.
Question 34:
Assertion (A): An electric motor will have maximum efficiency when back emf becomes equal to half of applied emf.
Reason (R): Efficiency of electric motor depends only on magnitude of back emf.
Question 35:
Assertion (A): The armature current in DC motor is maximum when the motor has just started.
Reason (R): Armature current is given by I = (E-e)/Ra
where, e = the back emf and Ra = resistance of armature
Question 36:
A thin semi-circular conducting ring (PQR) of radius r is falling s with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across the ring when its speed is v, is
(a) zero
(b) Bvπr2/2 and P is at higher potential
(c) πBv and R is at higher potential
(d) 2rBv and R is at higher potential
Question 37:
A wire loop is rotated in a magnetic field. The frequency of change of direction of the induced emf is
(a) once per revolution
(b) twice per revolution
(c) four times per revolution
(d) six times per revolution
Question 38:
An electric generator is based on
(a) Faraday’s law of electromagnetic induction
(b) motion of charged particles in electromagnetic field
(c) Newton’s laws of motion
(d) fission of uranium by slow neutrons
Question 39:
The inductance of a coil is proportional to
(a) its length
(b) the number of turns
(c) the resistance of coil
(d) the square of the number of turns
Question 40:
Which quantity is increased in step-down transformer?
(a) Current
(b) Voltage
(c) Power
(d) Frequency
Question 41:
A disc of radius 0.1 m is rotating with a frequency 10 rev/s in a normal magnetic field of strength 0.1 T. Net induced emf is
(a) 2π x 10-2 V
(b) π x 10-2 V
(c) π/2 x 10-2 V
(d) None of these
Question 42:
A rectangular coil of 20 turns and area of cross-section 25 cm2 has a resistance of 100 Ω. If a magnetic field which is perpendicular to the plane of the coil changes at a rate of 1000 T/S, the current in the coil is
(a) 1.0 A
(b) 50 A
(c) 0.5 A
(d) 5.0 A
Question 43:
Magnetic flux in weber in a closed circuit of resistance 10 Ω varies with time t(sec) as Φ= 6t2 – 5t+1. The magnitude of induced current at t= 0.25s is
(a) 0.2 A
(b) 0.6 A
(c) 1.2 A
(d) 0.8 A
Question 44:
A circular ring of diameter 20 cm has a resistance of 0.01 Ω. The charge that will flow through the ring, if it is turned from a position perpendicular to a uniform magnetic field of 2.0T to a position parallel to the field is about
(a) 63 C
(b) 0.63 C
(c) 6.3 C
(d) 0.063 C
Question 45:
A square metal wire loop PQRS of side 10 cm and resistance 1 Ω is moved with a constant velocity vc in a uniform magnetic field of induction B = 2 Wbm-2, as shown in figure. The magnetic field lines are perpendicular to the plane of the loop (directed into the paper). The loop is connected to net work ABCD of resistors each of value 3 Ω. The resistance of the lead wires SB and RD are negligible. The speed of the loop so as to have a steady current of 1 mA in the loop is
(a) 2 ms-1
(b) 2 x 10-2 ms-1
(c) 20 ms-1
(d) 200 ms-1
Answers:
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